The invention relates to a method of manufacturing golf balls. More specifically, the present invention relates to a method of heating golf balls prior to painting and the apparatus employed.
Conventional golf balls can be classified as one-piece, two-piece, and three-piece balls. One-piece balls are molded from a homogeneous mass of material with a dimple pattern molded therein. Two-piece balls are made by molding a cover about a solid core. Three-piece are typically, but not always wound balls which are made by molding a cover about a wound core. The core of a two-piece ball is typically formed of rubber and can be solid, semi-solid or have a liquid center. A wound core is prepared by winding a lengthy thread of elastic material about-the rubber core described above. The wound core is then surrounded with a cover material. The more recent trend in the golf ball art is towards the development of multi-component golf balls such as balls having two or more cover layers, two or more core layers or both multiple core and multiple cover layers.
Golf ball covers are presently formed from a variety of materials, such as balata, SURLYN(copyright), IOTEK(copyright), and polyurethane, depending upon the performance characteristics desired for the golf ball.
All golf balls, regardless of type, have an outer surface that contains a dimple pattern. As used herein, xe2x80x9cdimplesxe2x80x9d refer the topical relief of the outer surface of the ball, typically depressions or indentations formed into to provide desired aerodynamic effects. However, the dimple pattern may comprise of any form of topical relief on the outer surface of the golf ball formed to provide a desired aerodynamic effect to the ball, including formations such as protrusions from the outer surface.
Further to the above, golf balls are provided in a variety of colors. Conventionally they are white, but they may be manufactured in essentially any desired color, including yellow, orange and pink. The color is imparted to the ball either by applying layers of paint to the outer surface of the cover or by incorporating a pigment directly into the cover composition. Typically, in a painted ball, at least one primer layer is applied, followed by a second, finishing coat layer. After a ball has been provided with a color, identifying indicia such as a trademark, logo, identification number, model name or number and the like are hot stamped or pad printed onto the ball.
Golf balls must be capable of withstanding a variety of weather conditions such as strong sunlight, extreme temperature ranges, and immersion in water, preferably for an extended period. Further, the surface of a golf ball is flexed due to the impact every time it is struck with a club and consequently these surfaces must be able to withstand such repeated stresses. Moreover, especially with the recreational player, golf balls are susceptible to striking any of a number of hard, abrasive surfaces such as concrete, asphalt, brick, stone, etc. as a result of errant shots. It is therefore desirable for golf ball manufacturers that their golf balls be resistant to delamination or chipping of the paint layers, as such defects impact negatively upon the public perception of the quality of the golf ball. Likewise, golf ball manufacturers also seek to prevent obliteration of all or part of their trademarks, logos or other identifying indicia which identifies the brand of the ball to the playing public. Protective coatings are therefore applied to the surface of the golf ball cover. A clear primer coat and top coat layer are commonly applied to the cover to provide a high gloss and an overall enhanced appearance to the ball. In such coated balls, the various identifying indicia may be applied either to the cover, the primer coat or the topcoat.
Protective and decorative coating materials, as well as methods of applying such materials to the surface of a golf ball cover are well known in the golf ball art. Generally, such coating materials comprise urethanes, urethane hybrids, polyesters and acrylics. If desired, more than one coating layer can be used. Typical two pack polyurethane coatings include separate packages of polyol and diisocyanate. Conventionally, a primer layer such as a solvent-based or a water-based polymer may be applied to promote adhesion or to smooth surface roughness before the finish coat(s) are deposited on the golf ball. In general, a cured polyurethane top coat is most widely used as a protective coating material.
One problem encountered during golf ball coating is that each coat typically needs to be applied to the golf ball surface in a separate operation after the final molding of the golf ball cover about the core. Each of these steps is time consuming as once each coating is applied to the ball surface, there is a need to allow that coat to cure for a period of time before the next coat is applied. Also, as each of the often successive coats are applied to the golf ball, the definition of the curves on the molded golf ball are smoothed and lose their sharpness due to build-up of the coating composition on the ball""s outer surface, which also increases the outer diameter of the ball.
Typical paints used to coat golf balls, including urethane golf balls, comprise two component polyurethane coatings, which have good impact resistance. One of the problems associated with conventional two component polyurethane coatings is that they dry slowly.
Because of the slow drying nature of conventional polyurethane coatings, the golf ball painting process requires many steps. In the conventional process for clear-coating a golf ball, the surface-prepared balls are first mechanically loaded onto a stamping machine that prints a logo or stamp on the balls. The balls are then continuously loaded onto spindles that carry the balls and travel along with a moving chain to pass by spray guns that apply a clear polyurethane top-coating to the balls. The chain then moves wet, painted balls through a heated oven to pre-cure the coating. When they reach the end of the oven, the painted balls are usually still not dry, and have to be unloaded from spindles on the moving chain onto holding trays. The holding trays with the balls are then placed into another heated oven to bake at 105xc2x0 F. to 108xc2x0 F. for as long as 16 hours or in some cases even longer in order to completely cure the coating before further processing or handling. Due to the slow-drying nature of a conventional clear coat polyurethane system, all these steps, especially the 16 hour baking process, are usually necessary.
The conventional painting process has many drawbacks. First, loading wet balls from spindles on a moving chain onto holding trays, even if done by robotic handling, often results in damage or destruction of the surface of the balls.
Secondly, there is a substantial labor cost to unload cured balls from the trays into collecting hoppers for further processing. Thirdly, oven baking for 16 hours is time-consuming and consumes a substantial amount of energy. The ovens are large and require a large amount of floor space, which is also costly. The number of steps reduces productivity substantially.
In addition, an inevitable, substantial problem is that unloading wet balls off spindles onto loading trays often leaves balls with scratches or pin marks because the balls with wet paint have to be touched by another device. These scratches or marks are major causes of quality control rejection for surface defects.
For the foregoing reasons, there is a need for an improved process that will reduce the time for drying of the paint during the necessary steps. Further, there exists a need for an apparatus that will allow for a minimum of contact damage to the ball as it is supported on the apparatus.
One embodiment of the present invention provides for a process for heating a golf ball cover from about 90xc2x0 F. to about 150xc2x0 F. for 1 to 3 hours in a heated enclosure prior to applying a coat of primer or paint to the ball. This is done to accelerate the evaporation of paint solvents, immediately after the paint is applied. The painted balls are subsequently dried in a heated enclosure at about 105xc2x0 F. to 108xc2x0 F. All additional coats of primer or paint are applied in a similar fashion, wherein the balls are painted while still in the heated state and not cooled down.
An object of the invention is to reduce the flow of paint and the resulting blemish formed during the drying process. By reducing the contact area between the freshly painted ball and the drying tray holding them, the blemish is further minimized. This is accomplished by supporting the ball on a plurality of finely pointed conical pins during the drying process.
Another object of the invention is to provide a ventilated holding tray which in addition to holding the golf balls with a minimum of contact between ball and tray, the tray will allow for a thorough flow of heat about the ball for a quick and uniform heating of the ball.
Still another object in reducing blemishes to the golf ball, is suspending the freshly painted golf ball on conical pins set at right angles to the ball, thereby reducing physical contact between the tray and the freshly painted golf ball.
A further object of the invention is to provide a tray with replaceable ball supports or inserts. The inserts will generally be made from injection molded plastic and will be friction-fitted to the tray, and if damaged can be easily and inexpensively replaced. The pins being, recessed into the inserts, provides a considerable margin of safety when the tray is manually handled.